1. Field of the Invention
The present invention relates to a chuck apparatus for firmly fastening a tool in place.
2. Description of the Related Art
A conventional chuck apparatus for firmly fastening a tool has been proposed in U.S. Pat. No. 5,215,317 (hereinafter referred to a conventional example).
The conventional example is shown in FIG. 1 in which when a nut member 54 is rotated by rotating a sleeve 51, each claw 52 is advanced so that a diameter defined with the claws 52 is narrowed and the claw 52 is brought into contact with the tool. When the nut member 54 is not rotatable, the sleeve 51 is further rotated, a ring member 55 is rotated to thereby displace a relative position between the ring member 55 and the nut member 54.
As shown in FIG. 2, four recess portions 53 are formed in an annular form in a front end face (that is, in an end face on the side of the nut member 54) of the ring member 55. A slant surface 53a is formed on a bottom surface of each recess portion 53. As best shown in FIG. 3, the slant surface 53a is formed slantwise.
Accordingly, by rotating the sleeve 51 and advancing each claw 52 for narrowing a diameter defined with the claws 52, the claw 52 is brought into contact with the tool, and the nut member 54 is kept unrotatable. When the sleeve 51 is further rotated to rotate the ring member 55, each ball 56 that is in contact with the slant surface 53a is rolled and raised to the right side in FIG. 3, so that the nut member 54 is pushed forwardly by the slant surface 53a to thereby accelerate the fastening of the tool by the claws 52.
As a result of vigorous and continuous studies, the present inventor has found out the following disadvantages in the onventional example.
In the conventional example, until each claw 52 is advanced for narrowing a diameter defined therewith and brought into contact with the tool, the position of each ball 56 that has been located in a gauge 57 is not determined in the slant surface 53a. This is because there is a clearance in an axial direction of the nut member between each ball 56 and the nut member 54 located opposite the ball 56 due to the existence of the slant surface 53a of the recess portion 53. In particular, this clearance is large in the case where the ball 56 is located at the lowest position of the slant surface 53a or in the vicinity thereof (of course, the clearance is at maximum in the case where the ball 56 is located at the lowest position). The ball 56 is kept under the condition that it may be freely moved in the circumferential direction within the recess portion 53 due to the existence of the clearance. Accordingly, there is a condition that the ball 56 is not fixed to any position of the slant surface 53a. The instability of the position of the ball 56 would raise a problem that, in the case where the ball 56 is located at, for example, a position X in FIG. 3, the rolling rising amount of the ball 56 is small so that a sufficient increased fastening could not be attained.